U.S. Pat. No. 8,026,635 discloses a power sourcing equipment architecture (PSE) for variable maximum power delivery, excluding the architecture for a device comprising features of both a PSE and a powered device (PD). The power sourcing equipment architecture comprises an internal field-effect transistor (FET) and an external FET, which are controlled by a control switch, and allow variable amount of power delivery corresponding to a specific application. However, U.S. Pat. No. 8,026,635 does not disclose in detail the process to determine the amount of power required in the specific application.
FIG. 7 illustrates a detailed circuit schematic of Power over Ethernet (PoE) system 700 according to a prior art, where PSE 701 supplies power to PD 711 through Ethernet interfaces 702 and 712. DC power supply 703 generates output voltage that is applied across the respective center taps of Ethernet transformers 704 and 705. Ethernet transformers 704, 705, 714 and 715 include primary and secondary windings, where the center taps of the secondary windings of Ethernet transformers 704 and 705 are connected to voltage outputs of DC power supply 703, and the center taps of secondary windings of the Ethernet transformers 714 and 715 are connected to voltage inputs of DC power input 713. Ethernet transformers 705 and 704 pass data signals to and from Ethernet physical transceivers (Ethernet PHY) comprised in PSE 701 respectively. Lines 1, 2, 3, and 6 are used for supplying power to PD 711. Ethernet data, namely Rx Data and Tx data, are inputs and outputs to and from an Ethernet PHY respectively. The Ethernet data is transformer coupled and fully differential. The function of an Ethernet transformer, such as Ethernet transformers 704, 705, 714 or 715, is to isolate DC voltage from ports of Ethernet PHY(s).
The circuit of the PoE system described in the embodiments of the present invention, where power is supplied from a PSE to a PD, and Ethernet data is exchanged between the PSE and PD, is based on the ability of the Ethernet transformer to pass DC current through its center tap, and pass Ethernet data to Ethernet PHYs by isolating DC voltage from the ports of the Ethernet PHYs, as illustrated in FIG. 7.